Dark matter is as mysterious as it is ubiquitous. Cosmological evidence raises more questions than it answers about the origin and nature of the most abundant kind of matter in the Universe. Terrestrial experiments searching for answers have focused mainly on the possibility that the constituent of dark matter is a new particle near the Higgs boson mass scale - at the upper limit of the energy ranges ever explored in the laboratory. But recent years have seen a growing interest in the possibility that dark matter is made of particles in a far more pedestrian mass range, comparable to protons or electrons or somewhere in between. Such light dark matter particles could be hiding under our noses, kinematically easy to produce in the laboratory but difficult to detect because they are only produced rarely, through feeble interactions. I will discuss the theoretical underpinnings of sub-GeV dark matter, and the intriguing possibility that dark matter could be our first window into a "dark sector" with new particles and interactions. I will also discuss prospects for new small-scale experiments to explore these ideas, and the exciting prospect that the most strongly motivated parameter space is within reach of next-generation experiments.